1. Field of the Invention
The present invention relates to a focus detection device suitable for a camera.
2. Description of the Related Art
A phase difference CCD focus detection device, which is provided in a conventional AF single-lens reflex camera, includes line sensors and monitor sensors corresponding with a photographic optical system and focus detection areas.
A conventional CCD focus detection device outputs a first termination signal when an output signal of any of the monitor sensors reaches a predetermined threshold value, and outputs a second termination signal when output signals of all the monitor sensors reach the predetermined threshold value. Therefore, the level of the output signal of the monitor sensor cannot be detected.
There also exist some CCD focus detection devices that are provided with a monitor output terminal for externally outputting an output signal of the monitor sensor so as to test the characteristics of the monitor sensor. In order to process the output signal of the monitor sensor, which is output from the monitor output terminal, in a CPU provided for the camera, the CPU is required to have an exclusive A/D input port, or the like.